Madrid and Barca are massive clubs, the two biggest in the world, so just because players from the EPL leave to go play there ISNT because of the strength of the league. Nobody talented is going anywhere but those two.
Also the big two from Spain are people much the only destination for top EPL players as the English clubs usually will not sell to another English rival barring a MASSIVE upcharge and the only teams that can afford to "make it worth their while" to lose a their top player is only the big two from Spain. Everyone in Italy is broke, the Portuguese clubs are selling clubs, Munich has a monopoly on German players on the low so they typically dont need to spend big to get anyone, PSG is the only club in France with money like that since the Monaco owner's divorce, so that only leaves two clubs from Spain that can shell out what it takes to pry players like CR7, Bale, Suarez etc away from England.
Add that Madrid basically gets unlimited loans from Spanish banks to buy players and they as well as Barca have very skewed TV distribution rights compared to the rest of La Liga* (where in EPL tv revenue is pretty evenly for example) it is no wonder they are able to throw their weight around so well and buy the top talent.
* Warning: Spoiler! (Click to show)
Its a silly argument anyways, I enjoy both leagues and with how often this subject comes up with the same people arguing over and over on it I would hope you are on a payroll somewhere.
Different leagues different players, but at the end of the day its football. Enjoy it damn it!